To maintain electric power distribution “grids” in proper working order, it is important that the supply of electric power into the grid be maintained a safe margin above the demand caused by users of electricity from the electric grid. Because demand fluctuates it is important for the supply to also fluctuate so that the grid can maintain a safe margin of oversupply without the waste associated with excessive oversupply.
Some sources of electric power are necessarily intermittent, making their availability for peak power demand unreliable. For instance, solar power is only available during clear daylight hours. Wind power is only available when the wind is blowing.
Furthermore, some sources of electric power have lower costs than others. When demand is relatively low, it is desirable to have electric power demand met as completely as possible with low cost sources. When demand is high, however, the cost associated with the source is less critical, with higher cost sources still being beneficial to meet the demand.
Unfortunately, many lower efficiency (higher cost) combustion based electric power sources that are suitable for reliable use upon peak power demand are also relatively large emitters of atmospheric pollution. For instance, older coal fired power plants, older steam power plants which combust non-coal hydrocarbon fuels and diesel generators are generally relatively high volume emitters of atmospheric pollution per unit of electricity generated; and especially emitters of oxides of nitrogen, oxides of sulfur, volatile organic compounds, particulates, and other pollutants.
In many regions the atmospheric emission of pollutants is strictly controlled. Hence, even though power plants may exist and be available to meet peak demand on the electric grid, the high emissions of such lower efficiency combustion based power plants make their utilization undesirable (or legally precluded).
Accordingly, a need exists for low or no pollution sources of electric power which can be activated relatively quickly to meet peak electric grid power demand. While such systems benefit additionally from the highest electric power generation efficiency possible, the need for high efficiency is less critical in such peak demand situations, such that this need can be met with lower efficiency technology, especially when accompanied by lower capital costs to implement such systems.
One prior art system that has met this need to some extent is known as Compressed Air Energy Storage (CAES) provided by the CAES Development Company L.L.C. of Houston, Tex. (web site http://www.caes.net). With this prior art technology compressed air is stored in suitable large underground caverns. Air compressors use electric grid power during low demand periods to compress the air in the cavern. When high demand periods occur, the compressed air is used to combust fuel and generate a drive gas for a power turbine. CAES systems are limited by the need to be near an appropriate geological formation and have no low pollution benefit and so need to comply with more difficult emissions requirements.
Furthermore, when peak demand periods are encountered, it is important that existing power plants be in operation and operate to produce their highest possible power output. Many such power plants operate as heat engines that are variants on the Carnot Cycle, such as Brayton cycle gas turbine power plants and combined cycle power plants. Such power plants produce more power when an inlet air temperature is lower. However, often peak electric power demand occurs when air temperatures are highest, due to air conditioner loads. Thus, when needed the most, these heat engine power plants often suffer from somewhat reduced power output.
It is known that power output of a gas turbine may be augmented by chilling the turbine inlet air through techniques such as evaporative or refrigerative cooling. For instance, in one study entitled “Advantages of Air Conditioning and Supercharging and LM6000 Gas Turbine Inlet” in the Journal of Engineering for Gas Turbines and Power, July 1995, Vol. 117, Page 513, by Kolp, D. A., Flye, W. M. and Guidotti, H. A. it is claimed that reducing the inlet air temperature of a typical 40 MW gas turbine from 80° F. to 40° F. will raise the power output from 34 MW to 41 MW. However, for a refrigeration system to cool the air to this degree would require a large portion of the power saved and increase capital expenses to build such a plant.
Accordingly, a need exists for low emissions power generation that can be quickly started without concern for the presence of wind or sunlight to meet peak electricity demand. A need also exists to reduce air inlet temperatures of heat engine power plants to maximize their power output at times of peak electricity demand which coincide with high ambient air temperatures.